Vibration amplifier



Filed oct. 24. 1922 rais rara WALTER 'HHNEMANBL HEINRICH HECHB'HUGO LICHTE-AND LEONID DELMANN, 0F HELL GERMANY, .ASSIGNGRS T0 SIGNAL GESELLSCHAFT MET BESCHRNKTER HAFTUNG, 0F KIEL. GERMANY. A FIRM.

'VIBRATION AMPLIFIER.

The object of the invention is to provide an improved vibration ampli-tier of the microphone-telephone-type, i. r., of the type in which a microphone is actuated by vibrations of the mechanical vibratory structure or system of a telephone connected to a telephone line.

Generally speaking, the invention resides in certain improvements in the acousticrela tions of the vihratory parts of theelectromagnetic or the electrodynamic unit ot the telephone and ot the microphone, and in certain improvements in the balancing of the electrical circuits.

We shall new describe our invention in detail 'with reference to the accompanying drawings.

'n said drawings:

Figv l shows a Vibration amplifier in which the telephone is ot the electromagnetic type; y

Fig. f2 shows diagrammatically the aconstie relations ci the mechanically vibratory parts oi? the elcctromagnet land the microphone oiE Figure 1: and

Fig. shows a vibration amplifier in which the telephone is of the electrodyuaniic type. y

En the amplitierls'hown in Fig. l. the armature lv carried hy a diaphragm 3, and the magnetic Feld i together with the alternating current coil 7, represent the telephone system. The armature and field magnet are preferably formed of steel sheets in order to diminish the ordinary iron losses as much as possible.

The tvo poles of the Ulshaped magnet converge towards its ccntral axis. la consequence ot this it becomes possiblc to usc a smaller andthiclter armalnrc than usual in cooperation with a normal sized Umagnet. Such an armature is more advantageous because it has a smaller magnetic resistance than the nsnal long and flat armature of the ordinary j-magnet without having allarger mass.

The electro-magnet is rigidly seated in a recess in a coupling member 4. The diaphragm 3 which carries the armature 1 is also attacned to member 4, so that it acts as 4an elastic connection between the armature l and the member 4, permitting vibratory 59E-,648, and in Germany September 18, 1922.

movement of the armature toward and away from` the electromagnet.

The microphone is located in a recess in coupling member 4 at a point opposite the recess carrying the electromagne't. One electrode of the microphone is rigidly seated in member fl` although of course insulated therefrom; while the other electrode l1 is carried by the diaphragm 10,*nnd insulated therefrom by layer 13. 1 The space hetWeen-the electrodes 8 and ,l is filled with carbon granules 12, retained by retaining ring 9 ot yieldinginsulating material such as felt `or the like. The diaphragm i0 is secured at its periphcry to thc member 4, thus permitting vihratory movement ot the electrode trede 8.

It is to be mentioned that the elastic force of'the diaphragm l0 should preferably be great coinparcd to the inherent elastic force of thc volunic ot granulated carbon l2.' because the latter iu conscqucncc of its variability causes the natural t'rcqncncy ot the mechanical vibratory .structure rcprcscntcd by the microphone to vary. As a rulc` the elastic torccot the diaphragm should be at least threc quarters ot thc entire elastic force oi the mechanical vibratory structure represented by the microphone,

lt is sometimes dcsirablc to increase the damping 'of the mechanically vibratory structures or system 'of the apparatus.` This may be accomplished by incans of very shallow orilat air chambers or spaces. such as iand 24. preferably formed by the rigid plates 25 and QG respectively provided With 'small apertures 27. The air Within chambers Q3 and 24 is caused by the vibrations ot the diaphragms fl and l() to pass hack and forth through the small apertures or openings, thus causing friction anda damping ot the diaphragms.

The inicrophouc-telcphone-system of the amplifier is hung by means of rubber cords 22 within a casing 2l, being insulated by these cords against mechanical disturbances. The electrodes ot the microphone and the terminals of the alternating current coil are electrically connected to plugs attached to the Wall ofthe casing 21. n this Way an amplifier element is furnished, which may vl`l toward and away from elec-- easily be changed orfreplaced, similar t.; the well known vacuum tube amplifiers:

A iockingor securing device 29 serves 'to protectl the apparatus within the casing 2l from damage by shocks when it is not in use. To loch the apparat-us in the casing the loclr pin y30 is pushed down through guide sleeve or tube 33 to engage the apparatus and pressrit down toward block When the pin 30 is pushed. down so that the pin 32 projecting leterailytherefr'om is below the lower edge of sleeve 33, the pin 3Q 'is turned in 'the sleeve, thus moving pin 32 into locked position against the lower edge of sleeve 83.

We have found it advantageous to counterbalance the self-induction of the alternating Cil A rent coil of the amplier being proportioned current coil 7 by means of a capacity. Such a capacity is represented by the condenser C1. Similarly the self-induction of thev amplifier telephone l? may be counterbalanced vby another condenser C2. e

Such a' condenser., as for instance the conf denser C1, together with the alternating eurrent coil 'i' is an electrical oscillatory circuit of a definite natural frequency. If the natural frequency of a mechanical vibratory structure of the emplit ing apparatus is 'equal or about equal to tiat of this electric oscillatory circuit, a. multiple resonant system arises consisting of the electrical circuit and the mechanical structure.

lilith regard to the fact that. a condenser in the circuit of the coil 7 has the purpose of counter-balancing the self-induction of this coil, and with further regard to the fact that the value of this self-induction is greatest at a frequency of excitation lying a little below the frequency of resonance of the mecha-nical vibrator-y structure of the telephone systeni of the amplifier, it is to be preferred not tovequalize exactly the natural frequencies of this mechanical structureand the oscillatory circuit but to tune the latter toa pitch cor-- responding to the frequency at which the self-induction of the coil is the greatest'.

Another feature of the invention referring to the cooperation of an amplifier of the described kind with a given telephone line conssts in the alternating current resistance of the line and the alternating current resistance of the alternating current coil being equalized as far as possible. ln this way the ellicicncy of an amplifier' plant of this kind may be enhanced to a remarkable extent. lf the resistance of the line or f the combinationof apparatus in which the amplifier is to be used is known beforehand it can beconsidered in manufacturing the amplifier itself by the resistance of the alternating curto the alternating current resistance o plant. s

As to the acoustic features of the present invention., the apparatus of Fig. 1 embodies two mechanicallyv tuned vibratory structures.

- the naanoo? 'Each structure is made up of two masses connected by an elastic member. @ne of the structures is formed essentially of the arn'uu ture i as one mass; the electroanagnct G, the coil 7, and a portion of member fi, as (he other mass; and the diaphragm il as thc elastic connecting member. The other of the structures is formed essentially of the, cicctrode 1l as one mass; the electrode 8, and, a portion of member 4, as the other mass; and the diaphragm 10 as the elasticconnecting member.- llt will be seen from this that the member l acts as a mass common to 'both vibratory structures and couples them together.

The acoustic relations just vnientioncol'are illustrated diagrammatically in Fig. 2. In this ligure, the two vibratory structures are designated as' I and 1I. One structure is composed of mass m3, a portion of common mass 'm2, and elastic connecting member e2; the other structure is composed of mass m1, a portion of common mass m2, and elastic connecting member el. The designations m1, me, m3, 6 and e2, have been 'applied to Figure l on the drawings for the sake of clarity. According to the invention thetwo structures are each individually tuned to the same or nearly the same vfrequency andare then coupled together,A with a result substen tially analogous to that produced when two tuned electrical circuits are coupled together, in that a biresonant system is obtained, that is :he resonance curve of the coupled system has' two peaks. lin a coupled acoustic system suoli as shown in Fig. 2, the closenessor looseness of coupling depends upon the ratio between the common :nass and the' other masses. l/Ve have found it advantageous in the apparatus shown to have the common mass at least ten times as great as either of the other' two masses. Furthermore, the relative magnitudes of the masses determine the relative amplitudes of vibrations of the masses, so that it is possible to attain a dif ferent amplitude of vibration acting upon the microphone from that acting at the electrwmagnet.

The modification of the invention shown in Fig. 3 differs from Fig. l in that the armature of vthe 'electromagnet is replaced by a coil 18 which moves back and forth in. the

air space of a pot-shaped magnet-having a central pole piece 19.

1. ln apparatus of the character described, an electromagnet and an armature elastically connected together to form a tuned vibratory structure, and a microphone having its two electrodes elast-ically connected together to form a second tuned vibratory, structure, the

two vibratory structures being'coupled t0- gether. acoustically by meuis of a common mass, andthe masses of t e two vibratory structures being proportioned to secure larger amplitudes of vibration acting on the microphone than acting at the electromagnet.

2. A vibration amplifier unit comprising a vibrationamplifier element of the microplioue-tclephone-type with a magnetic field; a casing.. enclosing the amplifier element; elastic holders carrying the elen'lcnt within the casing; and a locking device securing the element within the casing when not used.

A vibration amplifier unit comprising a vibration amplifier element of the microphone-telephone-type with a magnetic field a "easing enclosing .the amplifier element; elastic-@holders carrying the element within the casing; and a locking device consisting of a stop pin.

4. In an apparatus of the character 'described a substantial, common mass including an electromagnet, an armature for said electromagnet elastically connected to-said common mass and a microphone elast-ically connected Vto said common mass, whereby said armature and said microphone are acoustically coupled by said common mass.

5. A vibration amplifier of the microphone telephone type comprising'a substantial comlmon mass including an electromagnet, an

armature for said electromagnet elastically connected to said common mass and a microphone having two electrodes, the space between which is filled with granulated carbon and means having a large elastic force as .compared with the elastic force re resented by the granulated carbon for coup ing acoustically said microphone to saidcommon mass.

6. In a vibration amplifier ofy the microphone telephone type, the combination-comprising two mechanical vibratoryv structures coupled together by acommon mass, one of.

the common mass including an elect-rode and i a second electrode mounted upon an elastic member and coupled acoustically to said common mass, the common mass being rela- 'tively large compared with the free masses.

7. In a vibration amplifier of the microphone telephone type the combination comprising two mechanical vibratory structures coupled together by a common mass. one of said structures comprising an armature mounted upon an elastic member and an electromagnet forming a part of said common mass and operating saidarmature, thc

other vmechanical vibratory structure com-- risin the common mass includin an elecy trode and a second electrode mounted upon an elastiemember, and coupled acoustically to said common mass, the common mass-he- .ing atleast ten times as large as one of the free masses and the free masses being about equal. :In testimony whereof we affix our signatures.

WALTER HAHNEMANN. HEINRICH HECHT. HUGO LICHTE.

LEONID ADELMANN. 

